A factory worker pushes a 30 kg crate a distance o...

A factory worker pushes a 30 kg crate a distance of 4.5 meters along a level floor at constant velocity by pushing it downward at an angle of 30 degrees below the horizontal. The coefficient of kinetic friction between the crate and the floor is 0.25.

a. What magnitude of force must the worker apply to move the crate at constant velocity?
b. How much work is done on the crate by this force when the crate is pushed a distance of 4.5 meters?
c. How much work is done on the crate by the normal force? By gravity?
d. What is the total work on the crate?